Blue energy or salinity difference energy takes advantage of the free energy released in the mixture of two
solutions with different salinity concentrations as it happens continuously in river mouths. Among the large
number of available techniques that aim to harness blue energy, capmix (or capacitive mixing) methods allow
to directly extract electrical energy without the need of any electromechanical converter such as turbines or
heat engines. The main goal of this article is to analyze the potential of blue energy by capmix methods in
Central America. So far, blue energy studies have been principally carried out in countries from the global
North. Therefore, we describe experimental results with real sea and river waters from the Gulf of Fonseca,
an area of special interest due to its hydrographic richness, which is situated among Honduras, El Salvador
and Nicaragua. An electrochemical cell, which consists of a pair of activated carbon electrodes coated with
cationic and anionic polyelectrolyte layers respectively, is used in the experiments. The cell voltage in open
circuit (OCV) is used as a measure of the performance of the capmix process. It is found that the OCV is
larger when natural river water is used instead of low salinity NaCl solutions. The rainy season in which
the experiments were performed reduced the ionic content of the river, increasing the salinity difference with
ocean waters. The feasibility of capmix as a means of clean energy production is discussed.